1. Field of the Invention
The present invention relates to an apparatus and associated method for the continuous, in vivo measurement of glucose in animal body fluids.
2. Description of the Prior Art
The detection and measurement of glucose in body fluids, such as blood, urine and cerebro-spinal fluid, provides information crucial to a proper assessment of the functions of the body. While hypo- and hyperglycemic conditions, which result from abnormal variations in blood glucose level, require prompt and accurate measurement in instances such as the administration of emergency medical attention to patients exhibiting these conditions, the need for an ongoing measurement of blood glucose levels is frequently necessary for patients with continuing diabetic conditions.
A variety of apparatus, including indwelling probes have been developed and tried, however these devices have proved wanting for specificity, and suffer from interference from other biological compounds. For example, Colton et al., Transplantation and Clinical Immunology, Volume X, Pages 165-173, Amsterdam (1978), disclose a system including an electronic glucose sensor, an insulin reservoir and pump, and electronics connecting the two. In this system, the sensor responds to rising glucose levels, and instructs the reservoir and pump to automatically dispense an appropriate quantity of insulin into the bloodstream. The sensor utilizes a platinum electrode catalyst for the purpose of oxidizing glucose therein. The use of the catalyst, however, results in reduced specificity of the electrodes, that exhibit interference with other metabolites, and resulting unreliability.
Soeldner et al., NIH Publication No. 76-854 (1976), at Pages 267-277, propose a glucose-sensitive implant electrode, that utilizes an immobilized quantity of the enzyme glucose oxidase, that by its action on available glucose in the blood stimulates an ion exchange that causes a corresponding differential incurrent that may be sensed and reported by the electrode. The mechanism of glucose oxidase activity with body fluid, it also used in a corresponding in vitro test, where the formation of hydrogen peroxide by the reaction of the enzyme, in the presence of a leuco dye, results in a visible color reaction. The invivo system of Soeldner et al. is deficient in that the enzyme glucose oxidase is unstable in this environment, and therefore is an unreliable determinant of glucose concentrations.
In my copending Application Ser. No. 241,991, the pertinent disclosure of which is incorporated herein by reference, a method and corresponding article for in vitro glucose monitoring is disclosed, which relies upon a glucose indicator comprising a reversible complex of a carbohydrate component, a binding macromolecular component and an indicator element bound to one of the components. In particular, the system utilizes a macromolecular component that may include carbohydrate-binding proteins such as lectins, that exhibit specific binding affinity for particular carbohydrates, and a continuum of carbohydrate oligomers of differing size, to offer a graded response to glucose concentrations. The disclosed system and method were primarily devised for use in in vitro monitoring wherein a sample of body fluid is abstracted and tested periodically to determine glucose levels therein.
A need is believed to exist for the development of an effective indwelling glucose monitor, that can offer continuous, in vivo-derived data regarding the dynamic condition of body fluid in terms of glucose concentration.